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Transversity and dihadron fragmentation functions

Transversity and dihadron fragmentation functions. Alessandro Bacchetta Regensburg University. Work funded by http://www.avh.de/ In collaboration with M. Radici, Università di Pavia. Outline. Introduction Dihadron FF to probe transversity Dihadron FF in DIS

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Transversity and dihadron fragmentation functions

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  1. Transversity and dihadron fragmentation functions Alessandro Bacchetta Regensburg University

  2. Work funded by http://www.avh.de/ • In collaboration with M. Radici, Università di Pavia A. Bacchetta - Dihadron fragmentation functions

  3. Outline • Introduction • Dihadron FF to probe transversity • Dihadron FF in DIS • Dihadron FF in e+e- annihilation • Dihadron FF in pp scattering A. Bacchetta - Dihadron fragmentation functions

  4. Why is fragmentation into two hadron interesting? • They can be used for TRANSVERSITY MEASUREMENT (the relative transverse momentum of the two hadrons can replace in single-pion production) • They reveal SPIN TRANSFER EFFECTS IN HADRONIZATION (the angular distribution of two hadrons can be sensitive to the spin of the quark) A. Bacchetta - Dihadron fragmentation functions

  5. Collinear single-hadron fragmentation The only relevant variable is the fraction of longitudinal momentum (z) p quark For unpolarized hadrons, the only fragmentation function at leading twist is A. Bacchetta - Dihadron fragmentation functions

  6. Noncollinear single-hadron fragmentation p The relevant variables are the fraction of longitudinal momentum (z) AND the transverse momentum quark For unpolarized hadrons at leading twist there are two fragmentation functions and Collins FF: relation between quark spin and kT A. Bacchetta - Dihadron fragmentation functions

  7. “Collinear” dihadron fragmentation No transverse momentum of the pair center of mass. h1 fraction of longitudinal momentum carried by the pair invariant mass of the pair polar angle of the hadrons in their center of mass frame azimuth angle of the pair plane quark h2 There are two fragmentation functions at leading twist: and A. Bacchetta - Dihadron fragmentation functions

  8. “Collinear” dihadron fragmentation No transverse momentum of the pair center of mass. h1 quark h2 Interference fragmentation function: relation between quark spin and RT A. Bacchetta - Dihadron fragmentation functions

  9. The dihadron interference fragmentation function is a chiral odd object that can be used to probe transversity • Collins, Heppelmann, Ladinsky, NPB420, 565 • Collins, Ladinsky, hep-ph/9411444 • Ji, PRD49, 114 • Jaffe, Jin, Tang, PRL 80, 1166, hep-ph/9709322 • Radici, Jakob, Bianconi, PRD 65, 074031, hep-ph/0110252 A. Bacchetta - Dihadron fragmentation functions

  10. h1 h2 _   quark quark h1 h2 Collins function h _   quark quark h Interpretation of function A. Bacchetta - Dihadron fragmentation functions

  11. Lz Lz-1 _ + Interpretation of function Cut-diagram representation Orbital angular mom. Quark helicity The orbital angular momentum projection has to change one unit, e.g. s-p wave interference p-p wave interference A. Bacchetta - Dihadron fragmentation functions

  12. Dependence on Considering only s and p waves (at low invariant mass) A. Bacchetta, M. Radici, PRD67, 094002 Each one of these functions contains different and interesting physics... A. Bacchetta - Dihadron fragmentation functions

  13. Dependence on Breit-Wigner shape See next talk by P. van der Nat R. Jaffe,X. Jin, J. Tang, PRL 80 (1997) Radici, Jakob, Bianconi, PRD 65, 074031 A. Bacchetta - Dihadron fragmentation functions

  14. Dihadron FF in semi-inclusive DIS l two-hadron plane l' y scattering plane z x A. Bacchetta - Dihadron fragmentation functions

  15. AUT asymmetry A. Bacchetta, M. Radici, PRD69, 074026 A. Bacchetta - Dihadron fragmentation functions

  16. Comparison with single-hadron l hadron plane l' y scattering plane z x A. Bacchetta - Dihadron fragmentation functions

  17. AUT in single-hadron production • Drawbacks: • Several terms • Convolutions • Evolution • Universality A. Bacchetta - Dihadron fragmentation functions

  18. Dihadron FF in e+e- annihilation Boer, Jakob, Radici, PRD 67, 094003 e- RCT PD P1D P1C RDT PC e+ A. Bacchetta - Dihadron fragmentation functions

  19. Dihadron FF in pp scattering PA F RCT RC SB P1C F PC SB PB Bacchetta, Radici, hep-ph/0409174 A. Bacchetta - Dihadron fragmentation functions

  20. Dihadron FF in unpolarized pp scattering Bacchetta, Radici, hep-ph/0409174 A. Bacchetta - Dihadron fragmentation functions

  21. Conclusions • Dihadron interference fragmentation functions are good candidates to “probe” h1(x) • They are easy to deal with from the theoretical and maybe also from the experimental point of view • They can be measured in SIDIS (HERMES, CLAS, COMPASS), in e+e- annihilation (BELLE, BABAR), in pp collisions (PHENIX, STAR, GSI, LHC, TEVATRON) A. Bacchetta - Dihadron fragmentation functions

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